1. Field of the Invention
The present invention relates to a method for the anticipated ascertainment of a bend on a portion of road taken by a motor vehicle and to a system for carrying out this method.
2. Description of the Related Art
The field of the invention is, generally speaking, that of motor vehicle headlamps. Known within this field are various types of headlamps, basically including:                parking lights, high-power lights and lights having a short range;        low-beam, or dipped, lights which are relatively powerful and have a road range of about 70 meters, which are used basically at night and the light beam of which is distributed so as not to dazzle the driver of an oncoming vehicle;        long-range, high-beam lights, and long-range-type complementary lights which have a range of vision on the road of about 200 meters and have to be switched off when passing another vehicle in order not to dazzle its driver;        advanced headlamps, known as bimodes, which combine the two functions of low-beam and full-beam lights by incorporating a removable screen;        fog lights, etc.        
The conventional headlamp devices which have just been described, more specifically those which are used as low-beam lights, produce light beams which are capable of improvement when these headlamp devices are used under specific conditions. Thus, for example, when a vehicle approaches a bend, the headlamps continue to illuminate straight ahead of them, whereas it would be more beneficial to orient the light beam in the direction of the bend to be taken. This is why, in addition to the conventional main headlamp functions, notably dipped and full-beam functions, various improvements have gradually appeared.
There have thus been developed sophisticated functions, known as AFS (advanced front lighting system) functions, including, notably, what is known as a DBL (dynamic bending light) function which produces an orientable headlamp device also known as a movable beam headlamp device: a headlamp device of this type is capable of modifying the orientation of a light beam produced by a light source in such a way that when the vehicle approaches a bend, the road is optimally illuminated by following the geometry of the road. (The term “headlamp device” refers to the headlamp itself or any other optical module movably mounted in a fixed headlamp.)
In order to implement such a function, a first known technology consists in allowing the main beam of the headlamp device to move by way of a motor which rotates as a function of an item of information originating from the vehicle, for example via a steering wheel angle sensor. The headlamp device is therefore said to be articulated. A second technology consists of a fixed light headlamp device comprising a plurality of light sources, for example of the light-emitting diode type, and means for controlling successive illumination of the sources as a function of the path of the vehicle so as to provide an effect in which light is swept toward the inside of an approaching bend.
With orientable headlamp devices of this type, the illumination of the road depends merely on the behavior of the driver. For example, if the driver turns the steering wheel of the vehicle toward the right, the headlamps of the vehicle are directed toward the right-hand side of the road in view of the fact that the bend extends to the right. Furthermore, the information relating to the change in direction is not sensed until the vehicle enters the curve of the bend, this information usually being provided by the steering wheel angle sensor detecting a variation in the angle of the steering wheel. The information is therefore supplied to the members monitoring the headlamp device only when the driver turns the steering wheel of the vehicle, when the vehicle has already entered the bend. As a result, the device is delayed on triggering of the lighting in the bend, thus resulting, for the driver, in a sense that the light beam has arrived late on entering the bend and in an excessively long return of the light beam in the axis of the vehicle on leaving the bend. This delay in the change of orientation of the headlamps not only is a source of discomfort for the driver but also compromises safety since there is, each time the orientation of the headlamps changes, a moment at which the road is insufficiently lit. The impossibility of detecting in advance a bend ahead therefore prevents optimum lighting of the bend in question.
In order to remedy these problems of non-anticipation, the prior art has proposed two types of solution.
A first type of solution consists in utilizing information derived from a navigation system.
A navigation system of this type combines information provided by a mapping system with indications given by the GPS of the vehicle. It allows the geometry of the road to be anticipated. For example, it is possible to be aware in advance of bends which will appear on the road in a given distance. It is therefore possible, by drawing on the information provided by the navigation system, to determine the distance separating the bend from the vehicle and also a radius of curvature of a bend which the vehicle is approaching and to orient at the appropriate moment, earlier than the foregoing solutions which have been described, light beams of the vehicle and thus to optimize the illumination of the bend. Devices of this type are described, notably, in patent applications EP 780 823, EP 887 229 and EP 1 415 856.
However, a certain number of defects inherent to the system limit the anticipation capacity thereof:                the current mapping is still very inaccurate. It frequently occurs that there is no information for a given place. Indeed, there are whole areas of the world which are not covered by the mapping databases;        the information provided by the navigation system may also be nonsensical. For example, if the driver planned to go to a place A which he has stored in his navigation system and if in the end, during his journey, he is led to go to a place B without following the indications given by the navigation system, then the items of information provided by this navigation system are inconsistent, or even contradictory, in relation to the path actually taken by the vehicle;        a loss of GPS coverage is also possible, for example when driving through a long tunnel or in an urban area with large buildings.        
A second type of solution consists in the utilization of information obtained by an image processing system. A system of this type utilizes at least one camera and image processing software applications. An example of a system of this type consists in a method for detecting white lines located on roads. However, there are not always white lines on a road and these white lines, if they exist, may be faded or covered by deposits of one type or another, such as earth; in this case, they can no longer be detected by the detecting method. Another example of a system of this type, described in document EP 1 431 918, consists in a method for detecting the curbs of roads. However, a method of this type is inadequate in various respects, especially if there is an intersection or junction on the road.
None of the existing systems is therefore entirely satisfactory for the anticipated detection of the characteristics of a bend which a motor vehicle is about to negotiate.